Hitherto, such organic silicon compounds as alkylalkoxysilane compounds and fluoroalkylalkoxysilane compounds have been known to be useful as surface treating agents, fiber treating agents, coating additives and the like. Especially, it has been known that when a fluoroalkylalkoxysilane compound is used to treat a surface of an inorganic material (for example, glass, metal, or oxide) for the purpose of controlling water repellency, oil repellency or sliding properties (slidability of droplets) of the surface, covalent bonds formed between the silyl group and the surface hydroxyl group of the inorganic material enable strong bonding between the fluoroalkylalkoxysilane compound and the inorganic material, whereby the weather resistance and retention of the modified surface properties are improved (“Silicone Handbook,” Edited by Itoh Kunio, Nikkan Kogyo Shimbun, Ltd., p. 79, line 9 to p. 80, line 5).
Alkoxysilane compounds are low in reactivity with the surface hydroxyl group of an inorganic material and, for improving this point, fluoroalkylsilazane compounds having a silazane structure have been developed (JP-B H07-094607).
Where a fluoroalkylalkoxysilane compound or a fluoroalkylsilazane compound is used for surface treatment, such a compound is very effective in improving the static contact angle representing water repellency and oil repellency. In this case, however, the angle at which a droplet starts sliding along the surface treated (sliding angle) as well as the hysteresis (θA−θR) obtained from the advancing contact angle (θA) and receding contact angle (θR) are high; in other words, the improvement in dynamic contact angle is insufficient. The dynamic behavior is particularly important as an index to sliding properties (droplet removal performance), and an improvement thereof is being requested.
In addition, as a compound which can impart water repellency and oil repellency to inorganic materials and which has high reactivity, there have been developed silazane compounds having a perfluoropolyether group (JP-A H02-011589). The silazane compounds, however, have been unsatisfactory in balance between the water and oil repellency and the sliding properties.